Weathering Steel in Bridge Replacement of Rail Overbridges · Corrosion allowance related to...

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Weathering Steel in Bridge Replacement of

Rail Overbridges27 November 2017

Weathering Steel in Bridge Replacement of Rail Overbridges

Outline

▪ Introduction

▪ What is Weathering Steel

▪ Benefits

▪ Design Considerations

▪ Recent Experience with Weathering Steel

▪ Nooroo Overbridge

▪ Michelago Overbridge

▪ Cooma Overbridge

▪ Conclusion

2


Introduction – NSW Timber Bridges

3

▪ 1,894 Council owned bridges

(2014 IPWEA)

▪ 950 in fair condition

▪ 504 in poor condition

▪ 83 Country Rail owned bridges

▪ Program of Bridge Replacements

▪ Improve safety

▪ Eliminate load capacity

restrictions

▪ Reduce maintenance

commitment

▪ New low maintenance structures


Bridge Replacement Options

4

▪ Proprietary Precast Concrete Modular

Bridge Deck Systems

▪ M-Lock® bridge system Rocla Span

7m to 15m

▪ HumeDeck® bridge system Span 6m

to 12m

▪ RMS Country Bridge Solution (CBS)

▪ Prestressed Concrete Double T-Deck

Modules – Span 8m to 12m

▪ PSC Planks

▪ RMS Planks – Span 6m to 18m

▪ QLD PSC Deck Units with Transverse

Stressing – Span 12m to 25m

▪ PSC Super-T Girders (T-Roff) – Span

18m to 37m


Bridge Replacement Options

5

▪ Steel Bridges

▪ Traditionally Not the first choice!

▪ Typically second consideration where weight and/or structural depth prevent the use of concrete

▪ As low as 5% of bridge designs in recent years

▪ Issues

▪ Ongoing maintenance of the protective coating

▪ Whole of life cycle costs

▪ INTRODUCTION OF WEATHERING STEEL WILL CHANGE THIS


What is Weathering Steel

6

▪ Structural steel alloy with enhanced

atmospheric corrosion resistance

▪ Uncoated it develops a stable protective

oxide coating, ‘Patina” which prevents the

steel’s tendency to continually rust

▪ Alloying elements include copper, chrome,

silicon, nickel and phosphorus

▪ Commonly referred to as COR-TEN®

(United States Steel Corporation) and

typically used for architectural panels,

screens and cladding applications

▪ BlueScope Steel now manufacture

structural plate from 10 to 80mm thickness

complying with AS/NZS 3678 Structural

steel – Hot-rolled plates, floor plates and

slabs


Weathering Steel

▪ BlueScope’s REDCORTM Weathering Steel

AS/NZS 3678-WR350 (B) (L0, L20)

▪ 10mm-80mm

▪ Chemical composition refined and engineered

to provide

▪ High steel toughness

▪ Good weldability

▪ Comparable alloy levels of standards for

weathering steels, ASTM A588 and A709 and

EN 10025 Part 5

▪ AS/NZS 3678-WR350 is a genuine high strength

structural plate grade

▪ Approx. 15% premium on material cost

7


Weathering Steel Bridges

▪ No Road/Rail public weathering steel

bridges in Australia

▪ Forestry Tasmania in 1990’s built

weathering steel plate girder

bridges

▪ First used worldwide:

▪ 1964 – USA, New Jersey Turnpike

▪ 1969 – Rail bridge in UK

▪ 2012 – KiwiRail replaced 4 underbridges

▪ Over 50 years of data on performance

8

Forestry Tasmania, 2013


Benefits of Steel

▪ Structural Benefits

▪ High strength to weight ratio

▪ Minimise structural depth

▪ Longer spans

▪ Variable structural depth

▪ Splice connections for continuous spans

▪ Less demand on substructure design

▪ Construction Benefits

▪ Lighter girders

▪ Rapid construction

▪ Fabrication off site in controlled workshop,

automated

▪ All steel is visible for inspection

9

Steel Innovations Conference 2013, Christchurch NZ


Weathering Steel vs Conventional Steel

▪ No protective coating

▪ Additional cost premium offset

▪ Quicker fabrication

▪ No coating maintenance

▪ Reduced whole of life cost

▪ No temporary scaffold

▪ No temporary lane closures

▪ Environmental benefits

▪ No VOC from oil based coatings

▪ No coating removal or containment of

particles

10


Benefit of Steel Bridge Replacement - Example

11

▪ Rail Overbridge replacement

over the North Coast Line

near Stroud, NSW



12

▪ Concrete PSC Plank deck units

with transverse stressing

adopted and designed



13

▪ Mass of plank 38 tonnes

▪ Required 300 tonne crane with a

gross mass of 72 tonnes

▪ Existing approach creek crossings

▪ Timber bridges structurally

inadequate

▪ Temporary propping required

▪ Environmental issues

▪ Re-design bridge with steel I-girders = less weight = smaller crane = no temporary propping



14

▪ Redesign with steel I-girders and composite

concrete deck including precast deck panels



15

▪ 1000WB322 Girders 8.5 tonnes



16


▪ Precast concrete formwork key

in achieving fast, simple and

safe deck construction

▪ Simplicity of design in steel,

precast concrete formwork and

composite cast in-situ deck was

such that overall $200,000

savings compared to concrete

PSC bridge



17


▪ Precast concrete formwork key

in achieving fast, simple and

safe deck construction

▪ Simplicity of design in steel,

precast concrete formwork and

composite cast in-situ deck was

such that overall $200,000

savings compared to concrete

PSC bridge

▪ ADDITIONAL BENEFITS IF

WEATHERING STEEL USED

▪ Whole of life cost less than

concrete bridge


Weathering Steel Design Considerations

▪ AS5100.6 (2017) weathering steel

requirements include;

▪ Corrosion allowance (Cl 3.7.2)

▪ Fatigue category (Cl 13)

▪ Welding consumables

(Appendix H4.2)

▪ Strength and serviceability

requirements no different

18

▪ Two key considerations for durable

weathering steel design;

1. Suitable Site Condition

2. Bridge Detailing


Weathering Steel Design Considerations

▪ Design References

▪ New Zealand Weathering Steel Guide for

Bridges: HERA Report R4-97:2005

▪ UK Design Manual for Roads and Bridges

Volume 2 Section 3 Part 8 – BD 7/01

Weathering Steel for Highway Structures

▪ FHWA Technical Advisory “Uncoated

Weathering Steel in Structures”

▪ BlueScope Information

▪ REDCOR™ weathering steel Product

Brochure

▪ Weathering steel Design Guide for Bridges in

Australia (HERA Guide)

▪ Technical Bulletin 26

▪ Technical Note – Guidance on the welding of

weathering steels

▪ Datasheet – AS/NZS 3678-WR350 (B) (L0,

L20)

19


Suitable Site Condition

▪ Atmospheric environment major factor in

formation and long term performance of

the patina

▪ NOT suitable environments include;

▪ Constant dampness, buried

▪ High chloride concentrations, coastal

environment

▪ High pollutant concentrations, industrial

area, corrosive fumes

▪ Directly over water bodies within 2.5m

(UK BD 7/01)

▪ Require constant wetting, drying cycles to

form adherent, stable patina

▪ Moisture day/night cycle

▪ Corrosion allowance related to

atmospheric environment and

classification

20


Atmospheric Classification

▪ AS4312 – Atmospheric corrosivity

zones in Australia

▪ Category C5 and C4 not suitable

▪ Category C3 Site specific studies

recommended

▪ Category C2 and C1 suitable

▪ Corrosion allowance as per

AS5100.6 (2017)

21

Category Corrosivity EnvironmentCorrosion

Allowance

C1 Very Low Dry indoors 1mm

C2 Low Arid / Urban Inland 1mm

C3 Medium Near Coast 1.5mm

C4 High Coastal N/A

C5 Very High Sea-Shore N/A


Bridge Detailing

▪ Drainage

▪ Steelwork can dry out, eliminate

moisture and debris retention, drip

plates on bottom flange

▪ Grind flush welds, terminate web

stiffeners above the bottom flange,

▪ Avoid expansion joints where possible

▪ Control run-off from steelwork, staining,

slope abutment headstocks, bearing

plinths and drip pans

22

NZ Guide HERA


Bridge Detailing

▪ Welding

▪ Weathering steel has similar welding

characteristics to conventional

structural steel

▪ AS/NZS 1554.1 is applicable

▪ Welding consumable selection

▪ Welding consumables from Table

4.6.1(C) of AS/NZS 1554.1 providing

consistent corrosion and colouring

▪ BlueScope Technical Bulletin 26

Weathering Steel

▪ BlueScope Technical Note on the

Welding of Weathering Steels

▪ Bolting

▪ Galvanic reaction, zinc galvanised bolts

sacrificed

▪ Weathering grade bolts to ASTM A325

Type 3 equivalent to property class 8.8

23


Bridge Detailing

▪ Aesthetics

▪ Colour and texture varies over time

▪ Initially orange-brown as the patina develops to the uniform characteristic dark brown

▪ Post fabrication blast clean with non-metallic grit

▪ Urban design aspect is subjective

24

2 months 1 year 29 yearsNSSMC website


Recent Experience – Nooroo Overbridge

▪ Overbridge on Nevilles Road at

263.816km over the North Coast Line

▪ Jacobs appointed by JHR-CRN to provide

design for the replacement

▪ Existing timber bridge 22.9m length and

3.8m width

▪ New low-maintenance structure that

meets the needs of the asset owner and

the local government authorities

▪ Preferred Option - composite weathering

steel I-girder superstructure with precast

deck panels

25

▪ Construction methodology

▪ Lighter girders

▪ Comparable whole of life cost



26

▪ Overall deck length of 20.67m and width

between barriers of 4.5m

▪ 3 x 1024mm deep I-girders AS/NZS 3678-

WR350 at 2.0m c/c

▪ 400 x 32 thick top flange

▪ 16 thick web

▪ 400 x 32 thick bottom flange

▪ Precast concrete 125mm thick formwork

full width panels that include upturns on

each side to act as formwork for the in-situ

concrete traffic barrier.

▪ 125mm thick in-situ concrete slab to form

a total 250mm concrete deck.



▪ Atmospheric corrosivity category is

C2: Low in accordance with AS 4312

▪ Bridge site approx. 42km from coast

▪ Topography provides shielding from

salt spray

▪ Rural and remote from sources of

pollution

▪ Adopted a 1.0mm per exposed face

corrosion allowance

27

Nooroo



▪ Bridge detailing adopted includes

▪ Concrete plinths to avoid any debris

retention

▪ Intermediate stiffeners minimised

▪ Drip plates at low end of outer girders

to deflect any runoff and prevent debris

accumulation

▪ Sloping abutment to control run-off

▪ Fully sealed small movement joints

▪ Stainless steel drip pan to protect the

laminated elastomeric bearings

28



▪ Precast concrete deck panel

▪ Fully decked to provide a safe working

platform during construction

▪ Upturns on each side to act as formwork for

the in-situ concrete traffic barrier

▪ Ease of construction over rail line during

track possession

▪ Mass of panel 6.8 tonnes

▪ Formed holes within deck panel for

groups of shear studs

▪ AS5100.6 requires complete shear

interaction

▪ Spacing and size of voids balanced with

concrete width required for strength

29


Recent Experience – Michelago Overbridge

▪ Overbridge on Kelly Road at 363.533km

over the Goulburn to Bombala Line



▪ Existing timber bridge 20.1m length and

7.1m width

▪ New low-maintenance structure that meet

the needs of the asset owner and the local

government authorities


steel I-girder superstructure with integral

abutments

30

▪ Low maintenance structure

▪ Lighter girders




31


between barriers of 8.0m


WR350 at 2.4m c/c


▪ 16 thick web


▪ Composite concrete deck of 265mm

overall thickness, 75mm thick precast

‘Humeslab’ and 190mm thick in-situ

▪ Full height precast concrete bridge

barriers



▪ Atmospheric corrosivity category is C2: Low in accordance with AS 4312

▪ Bridge site >50km from coast

▪ Rural and remote from sources of pollution

▪ Adopted a 1.0mm per exposed face corrosion allowance

32

Michelago



▪ Bridge detailing

adopted includes

▪ Intermediate

stiffeners minimised

▪ Drip plates at low end

of outer girders to

deflect any runoff and

prevent debris

accumulation

▪ Integral connection

eliminates any runoff

issue through joints

33


Recent Experience – Cooma Overbridge

▪ Overbridge on Thurrung Street at

432.700km over the Goulburn to Bombala

Line



▪ Existing Bailey Bridge 21.35m length and

3.57m width between trusses and 6.27m

overall width with the pedestrian walkway.

▪ New low-maintenance structure that meet

the needs of the asset owner and the local

government authorities


steel I-girder superstructure with integral

abutments

34

▪ Low maintenance structure

▪ Lighter girders




35


between barriers of 11.0m incl. shared use

path


WR350 at 2.0m c/c (braced in pairs to

assist with stability in transportation and

erection)


▪ 16 thick web


▪ Precast concrete deck panels providing

total a total 250mm composite concrete

deck



▪ Atmospheric corrosivity category is C2: Low in accordance with AS 4312

▪ Bridge site >50km from coast

▪ Rural and remote from sources of pollution

▪ Adopted a 1.0mm per exposed face corrosion allowance

36

Cooma



▪ Bridge detailing adopted

includes

▪ Intermediate stiffeners

minimised

▪ Drip plates at low end of

outer girders to deflect any

runoff and prevent debris

accumulation

▪ Integral connection eliminates

any runoff issue through

joints

37


Weathering Steel Opportunities

▪ Composite Weathering Steel

Superstructure

▪ Longer spans

▪ Variable depth

▪ Splice connections for continuous

spans

▪ Eliminate heavy concrete girders

▪ Less demand on substructure design

38

Modern Steel Construction March 2012


Conclusion

• The availability of weathering steel in

larger plate sizes from BlueScope

Steel warrants the use of steel bridge

designs to be revisited for Rail

Overbridges

• We have demonstrated that

weathering steel bridges can be cost

competitive against concrete

alternatives

• We hope this will generate discussion

and exchange of ideas for weathering

steel bridges

39


Acknowledgements

• John Steele – Jacobs Technical Director Bridges

• Felix Lie – Jacobs Bridge Engineer

40

www.jacobs.com | worldwide27 November 2017

© Copyright Jacobs

Weathering Steel in Bridge Replacement of

Rail Overbridges

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